A Guide to Noxious & Invasive Species
Japanese Knotweed, Giant Hogweed, Himalayan Balsam and other invasive & noxious species.
In the UK, we are home to a range of native and non-native species that can cause more than just aggravation to homeowners. In some instances, these weeds can cause structural damage to property, affect its value and cause harm to both humans and natural habitats of wildlife.
In this article, we look at some of the more well known species and examine the difference between invasive and noxious species.
Invasive Species
Japanese Knotweed (Fallopia japonica)
Native to: Japan, Taiwan, Northern China
As, perhaps the most commonly known invasive specie, Japanese Knotweed was originally brought to the UK as a decorative plant in the early 19th century, given its white flower which blooms in spring and summer. Unfortunately, this non-native specie spreads rapidly in the wild, by both natural means and as a result of human spread. Commonly found alongside roads, railways and watercourses, the plant forms thick, dense colonies that can easily overcrowd and outcompete neighbouring native species.
Japanese Knotweed is listed under Schedule 9 of the Wildlife and Countryside Act 1981 with respect to England, Wales and Scotland. This means it is an offence to plant or otherwise cause Japanese Knotweed to grow in the wild.
Stopping the spread of Japanese Knotweed
There are a number of methods to stop the spread of Japanese Knotweed, but it is always advised to seek professional advice and services of those specialising in treating Knotweed.
Herbicide Application
Possibly the most effective method consists of either spraying the plant or injecting the stems with specialist herbicides. A course of treatments will be required, sometimes taking at least 3 years to treat the Japanese Knotweed effectively. It is worth noting that Knotweed rhizomes can remain dormant in the soil for many years, and will regrow if disturbed or if the soil is relocated.
Physical Removal
Sometimes known as ‘dig and dump’ this method is used if there are time constraints onsite. Here, contaminated soil from the site is removed and disposed of via registered landfill. When carried out correctly this method will remove all Japanese Knotweed from site, allowing for groundworks to commence immediately. All relevant legislation must be adhered to during this process as it is critical that all of the plant is removed with absolutely no cross site contamination.
Himalayan Balsam (Impatiens glanduifera)
Native to: West and Central Himalayas
Often found on river banks and in damp woodland, this tall, attractive, annual herb was introduced as a garden plant in the early 19th century and first recorded in the wild in 1855. During the growing season, it is easy to identify as a mature plant with its pink-purple flowers and fleshy stem. It's usually favoured by the general public due to its aesthetic appeal and is sometimes deliberately planted for this reason.
Now widespread in the UK, Himalayan Balsam thrives along urban rivers and is spread solely by its seeds, which are small and easily carried by the wind or water. The plant can grow up to 2m in height and often grows densely along river banks, sometimes impeding the flow at times of high rainfall and therefore increasing the likelihood of flooding. During the winter months the die back can be extensive leaving river banks bare and exposed to erosion.
Effective Himalayan Balsam Management
Herbicide Application
Effective control can be carried out via herbicide application and should ideally be sprayed in the spring, before flowering, but late enough to ensure that germinating seedlings have grown up sufficiently to adequately absorb the herbicide.
Himalayan Balsam is listed under Schedule 9 to the Wildlife and Countryside Act 1981 with respect to England, Wales and Scotland. This means it is an offence to plant or otherwise cause Himalayan Balsam to grow in the wild.
Giant Hogweed (Heracleum mantegazzianum)
Native to: South West Asia
Introduced by the Victorians, Giant Hogweed was first recorded in Cambridgeshire and was deliberately planted by rivers and ponds due to its ability to grow in lowlands across the entire British Isles. Since its introduction, it has been spreading rapidly despite the various control measures in place. In addition to riverbanks, it is regularly spotted alongside roads and railway lines.
A member of the cow-parsley family, its flowing stems are typically 2-3 metres in height and bear flower heads of up to a 80cm radius. Being monocarpic (reproducing only once in its lifetime), Giant Hogweed reproduces entirely by seeds. The plants are able to self-fertilise, with each plant producing 20-50,000 seeds and in some cases surviving more than 3 years in the soil.
It is very important to note that the sap of the plant is phototoxic, meaning it causes serious skin burns under sunlight, so if you do come across Giant Hogweed, do not touch it!
Effective Giant Hogweed Management
Herbicide Application
Herbicide application is the most effective treatment method and is generally carried out in the spring and early summer and involves multiple visits between March and July, to ensure follow up treatments are applied to any late emerging or missed plants.
Giant Hogweed is listed under Schedule 9 to the Wildlife and Countryside Act 1981 with respect to England, Wales and Scotland. This means it is an offence to plant or otherwise cause Giant Hogweed to grow in the wild.
For more information on how WeedWise can help with management of invasive and noxious species, please get in touch via the information below:
0800 074 0931